Grounds need to be common to all components: Photon, LCD, pressure transducers, alarm

LCD
RX to Photon TX
Vin – YwRobot +5V. Must be a minimum of 5V. Don’t parallel off Photon, it works but LCD is barely readable.
GND – from common ground source.

Photon
Power via micro-usb port from YwRobot USB port
Pin D0 – to alarm. I was going to use a single relay but have found a controllable buzzer. If it is loud enough I will use it.
A0 – bathroom gray tank pressure sensor
A1 – kitchen gray tank pressure sensor
A2 – black tank sensor
A3- fresh water tank sensor
Ground – Common tie to LCD ground and alarm (or relay control ground if a relay is used.
TX – LCD RX